Actually had a funny one the other day.
Random London number called and answered with the typical few "Hello.... Hello?.... Uhhh hello" before any response. Then get some guy saying something but the audio level was too low to make out what he was saying (checked my level at it was maxed). So asked politely for them to repeat as I couldn't really hear.
The voice comes back with "can you hear me m8?" so I respond "yes but barely, the line is really quiet" and also the seemed to be a lot of chatter in the background.
I then got the reply "oh **** off" and they hung up. Was a bit miffed at this so I called back and the line was fine but sounded like someone else so said I had been called and want to talk to a manager. Spoke to the guy and explained and he said he'd check the call logs and speak to the person and seemed genuinely apologetic as he was a training manager so obviously they try to get them not to swear at customers

and then took my name off their list and went about my day